Magnetic radial bearing with flux boost

ABSTRACT

A magnetic bearing (20) comprises: a rotor (22) to be supported for rotation about an axis (502); a stator (24) extending from a first end (30) to a second end (32) and comprising: one or more first permanent magnets (50); one or more second permanent magnets (52) of polarity substantially opposite to a polarity of the one or more first permanent magnets; and laminate teeth, encircled by radial windings (36A, 36B), axially between and extending radially inward of the one or more first permanent magnets on one side and the one or more second permanent magnets on the other side. The rotor comprises: one or more third permanent magnets (150); and one or more fourth permanent magnets (152) axially spaced from the one or more third permanent magnets.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. Patent Application Ser. No. 62/480,405, filedApr. 1, 2017, and entitled “Magnetic Radial Bearing with Flux Boost”,the disclosure of which is incorporated by reference herein in itsentirety as if set forth at length.

BACKGROUND

The disclosure relates to magnetic bearings. More particularly, thedisclosure relates to electromagnetic bearings utilized inturbomachines.

A well-developed art exists in active magnetic bearings. US PatentApplication Publication 2011/0163622A1 (US '622), published Jul. 7,2011, discloses an electromagnetic bearing providing radial and axialsupport. For axial support, the stator has a pair of opposite axialpoles joined at an outer diameter (OD) by an axial back iron. An axialcoil circumferentially wraps inboard of the back iron and creates a fluxpath through the axial poles and back iron with an inboard gap betweenthe axial poles spanned by an actuator target formed by a rotorlamination stack within the gap.

Generally, radially inboard of the axial coil, the US '622 statorcomprises a radial actuator pole assembly formed by a lamination stack.This lamination stack has a full annulus outer ring portion and aplurality of radially-inward projections each of which is wrapped by anassociated radial control coil. Adjacent the radial actuator poleassembly at opposite axial ends thereof, sandwiched between the radialactuator pole assembly and the axial poles, are a pair of permanentmagnetic rings.

Generally, a pair of radial flux loops are created at opposite sidesproceeding radially from the US '622 actuator target through the radialpole assembly, turning axially outboard through the permanent magnet andthen radially inboard through the associated axial pole, turning backaxially inward to enter the end of the actuator target and then turningback radially outward. Thus, a pair of radial fluxes of opposite signare encircled by the axial flux loop.

Another four-radial-pole radial bearing configuration involves fluxpaths that pass radially and circumferentially rather than axially. Inthis configuration, switching can be between several conditions. Onegroup involves flux paths with a central diametric leg through oneopposed pair of poles and two circumferential legs passingcircumferentially through the back iron around the respective poles ofthe other pair. The two pairs thus create two possible such paths withtwo possible directions for each path. Additionally another groupinvolves a first flux path leg passing radially through one pole,turning circumferentially to pass through the back iron to one of thetwo adjacent poles and then returning back radially through thatadjacent pole to meet the first leg in the shaft.

PCT/US2016/017943, filed Feb. 15, 2016 and entitled “Magnetic Bearing”and published Sep. 1, 2016 as WO/2016/137775 (the WO '775 publication),the disclosure of which is incorporated by reference herein in itsentirety as if set forth at length, discloses a magnetic radial/thrustbearing utilizing permanent magnet bias and electromagnet bias.

U.S. Patent Application No. 62/381,746, filed Aug. 31, 2016, andentitled “Magnetic Thrust Bearing”, the disclosure of which isincorporated by reference herein in its entirety as if set forth atlength, discloses a magnetic thrust bearing combining permanent magnetbias and electromagnet bias.

SUMMARY

One aspect of the disclosure involves a magnetic bearing comprising: arotor to be supported for rotation about an axis; a stator extendingfrom a first end to a second end and comprising: one or more firstpermanent magnets; one or more second permanent magnets axially spacedfrom the one or more first permanent magnets; a plurality of laminateteeth axially between and extending radially inward of the one or morefirst permanent magnets on one side and the one or more second permanentmagnets on the other side; and a plurality of radial windingsrespectively encircling a respective associated tooth of the pluralityof teeth. The rotor comprises: one or more third permanent magnets; andone or more fourth permanent magnets axially spaced from the one or morethird permanent magnets.

In one or more embodiments of the other embodiments, the one or morefirst permanent magnets and the one or more second permanent magnets arenon-rare earth magnets.

In one or more embodiments of the other embodiments, the one or morethird permanent magnets and the one or more fourth permanent magnets arenon-rare earth magnets.

In one or more embodiments of the other embodiments: the one or moresecond permanent magnets have a polarity substantially opposite to apolarity of the one or more first permanent magnets; and the one or morefourth permanent magnets have a polarity substantially opposite to apolarity of the one or more third permanent magnets.

In one or more embodiments of the other embodiments: the one or morethird permanent magnets have a polarity substantially opposite to apolarity of the one or more first permanent magnets; and the one or morefourth permanent magnets have a polarity substantially opposite to apolarity of the one or more second permanent magnets.

In one or more embodiments of the other embodiments, the one or morefirst permanent magnets and the one or more second permanent magnets arefull annulus.

In one or more embodiments of the other embodiments, the one or morethird permanent magnets, the one or more fourth permanent magnets arecircumferentially segmented.

In one or more embodiments of the other embodiments, the magneticbearing is a non-thrust bearing.

In one or more embodiments of the other embodiments, the stator furthercomprises: a center yoke radially surrounding the plurality of teeth; afirst end yoke axially abutting the one or more first permanent magnets;and a second end yoke axially abutting the one or more second permanentmagnets.

In one or more embodiments of the other embodiments, the stator furthercomprises: a first end laminate encircled by the first end yoke; and asecond end laminate encircled by the second end yoke.

In one or more embodiments of the other embodiments, the rotor furthercomprises: a center laminate axially between the one or more thirdpermanent magnets and the one or more fourth permanent magnets.

In one or more embodiments of the other embodiments, the center laminatehas an inner diameter (ID) surface radially outboard of respective innerdiameter (ID) surfaces of the at least one third permanent magnet andthe at least one fourth permanent magnet.

In one or more embodiments of the other embodiments, the rotor furthercomprises: a first end laminate axially abutting the one or more thirdpermanent magnets; and a second end laminate axially abutting the one ormore fourth permanent magnets.

In one or more embodiments of the other embodiments, the rotor first endlaminate has an inner diameter surface radially inwardly converging inan outward axial direction; the rotor second end laminate has an innerdiameter surface radially inwardly converging in an outward axialdirection. At least one of: (a) the one or more third permanent magnetsand one or more fourth permanent magnets have respective axial outboardsurfaces radially inwardly converging in a respective outward axialdirection; (b) the rotor comprises: one or more first steel piecesforming a frustoconical ring intervening between the one or more thirdpermanent magnets and the rotor first end laminate; and one or moresecond steel pieces forming a frustoconical ring intervening between theone or more fourth permanent magnets and the rotor second end laminate;and (c) the rotor comprises: one or more first end magnets forming afrustoconical ring intervening between the one or more third permanentmagnets and the rotor first end laminate and having a less axialpolarity than the one or more third permanent magnets; and one or moresecond end magnets forming a frustoconical ring intervening between theone or more fourth permanent magnets and the rotor second end laminateand having a less axial polarity than the one or more fourth permanentmagnets.

In one or more embodiments of the other embodiments, a method for usingthe magnetic bearing comprises running current through the plurality ofradial windings so as to control radial position of the rotor.

In one or more embodiments of the other embodiments, the plurality ofradial windings comprises a diametrically opposite first pair ofwindings and a diametrically opposite second pair of windings orthogonalto the first pair of windings.

In one or more embodiments of the other embodiments, the first andsecond pairs of windings are each powered by a respective associatedH-bridge amplifier.

In one or more embodiments of the other embodiments, for each winding ofthe first pair of windings and the second pair of windings: a firstpermanent magnet flux paths passes as a loop through the winding, the atleast one first permanent magnet and the at least one second permanentmagnet; and a second permanent magnet flux paths passes as a loopthrough the winding, the at least one second permanent magnet and the atleast one fourth permanent magnet. The running current comprises runningcurrent through one winding of the first pair of windings to augment theassociated first and second permanent magnet flux paths while runningcurrent through the other winding of the first pair of windings tocounter the associated first and second permanent magnet flux paths.

In one or more embodiments of the other embodiments, the running currentcomprises: running current through one winding of the second pair ofwindings to augment the associated first and second permanent magnetflux paths while running current through the other winding of the firstpair of windings to counter the associated first and second permanentmagnet flux paths.

In one or more embodiments of the other embodiments, a machine comprisessuch a bearing.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, partially schematic, central longitudinal axialsectional view of an electromagnetic bearing in a compressor.

FIG. 2 is a transverse sectional view of the bearing taken along line2-2 of FIG. 1.

FIG. 3 is a transverse sectional view of the bearing taken along line3-3 of FIG. 1.

FIG. 4 is a transverse sectional view of the bearing taken along line4-4 of FIG. 1.

FIG. 5 is a transverse sectional view of the bearing taken along line5-5 of FIG. 1.

FIG. 6 is a transverse sectional view of the bearing taken along line6-6 of FIG. 1.

FIG. 7 is a schematic central longitudinal sectional median magneticflux diagram showing permanent magnet flux.

FIG. 8 is a schematic central longitudinal sectional median magneticflux diagram showing combined permanent magnet and electro-magnet flux.

FIG. 9 is a schematic view of an H-bridge amplifier used to power one ormore coils.

FIG. 10 is a partial, partially schematic, central longitudinal axialsectional view of a first alternate electromagnetic bearing in acompressor.

FIG. 11 is a partial, partially schematic, central longitudinal axialsectional view of a second alternate electromagnetic bearing in acompressor.

FIG. 12 is a partial, partially schematic, central longitudinal axialsectional view of a third alternate electromagnetic bearing in acompressor.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows an axial homopolar bearing 20 having a rotor 22 and astator 24. The stator has a central longitudinal axis 500. The rotor hasa central longitudinal axis 502. The axes 500 and 502 are nominallynormally coincident; however, the bearing may absorb slight excursionsof the rotor axis relative to the stator axis. The magnetic bearing maybe used in a turbomachine (e.g., a compressor) wherein the stator ismounted to (or otherwise integrated with) a housing or case of thecompressor and the rotor is mounted to (or otherwise integrated with) ashaft of the compressor. A stator transverse centerplane is shown as 510and the normally coincident rotor transverse centerplane is shown as512. For purposes of schematic illustration, the housing or case isshown as 26 and the shaft is shown as 28. Exemplary compressors arecentrifugal compressors.

The bearing extends from a first end 30 to a second end 32. The statorincludes a number of coils (e.g., metallic wire windings). As isdiscussed further below, the exemplary bearing is a purely radialbearing and not an axial or thrust bearing. Alternative implementationsmay integrate with axial bearing features. Also, the exemplaryembodiment is mechanically symmetric end-to-end about the centerplane510, 512. It may also be grossly electrically symmetric (e.g., theoverall layout of the coils is symmetric) but the wrapping of the coilsand the electrical connections may be asymmetric in order to provide thecontrol described.

In the exemplary radial bearing, there are four coils: two orthogonalpairs of two diametrically opposed coils. In the X-Y frame of referenceshown in FIG. 2, there is a pair of X coils 34A, 34B and a pair of Ycoils 36A, 36B. FIG. 2 further shows a local radial gap 38 between rotorand stator. As is discussed further below, in operation magnetic fluxcrosses the gap 38 at various locations to exert a net force on therotor. Energizing the X coils in one way exerts a force in the positiveX direction and energizing X coils in the opposite way exerts a force inthe negative X direction. Similarly, energizing the Y coils in one wayexerts a net force in the positive Y direction and energizing the Ycoils in the opposite way exerts a force in the negative Y direction.Control may be responsive to conventional radial position sensors (notshown) integrated with or otherwise associated with the bearing. Theexemplary coils in a given pair may be electrically connected in seriesor controlled separately so that currents through them create a radialcontrol field that either opposes or assists a permanent magnet biasfield (discussed below).

The stator comprises a first permanent magnet ring 50 (FIG. 1) and asecond permanent magnet ring 52 coaxially axially spaced apart from eachother. The permanent magnet rings have substantially opposite axialpolarity. In this example, the north poles of both magnets face theinward to the transverse centerplane 510 and the axially-opposite southpoles face axially outboard/outward. The magnet rings may be fullannulus continuous rings or may be segmented (discussed below).Manufacturing tolerances will mean that exact opposite polarity may notbe achieved. Typically, this will be achievable within 20° or within10°. Some alternative configurations may involve intentionally shiftingthe polarities somewhat off axial so that they may be up to an exemplary60° off anti-parallel.

Each ring 50, 52 has an inner diameter (ID) face (surface), an outerdiameter (OD) face (surface), and opposite axial end faces (surfaces).The rings 50 and 52 are mounted at opposite sides (axial ends) of acentral back iron or yoke 60. The exemplary central back iron 60 (andother back irons or yokes discussed below) is formed of a non-laminatemagnetic steel such as 1010 steel. The exemplary central back iron isformed as a continuous full annulus single piece rather than segmented.The central back iron 60 has an ID face and an OD face and oppositeaxial end faces. Extending radially inward from the ID face are aplurality of laminate teeth (FIG. 2) 64A, 64B, 66A, 66B respectivelyassociated with and encircled by the coils 34A, 34B, 36A, 36B. Exemplarylaminates (and other laminates discussed below) are axial stacks ofsteel plates (e.g., soft magnetic steel or silicon steel). Use oflaminate reduces eddy loss relative to a single block of steel. Thelaminate within the coils functions as a core.

The exemplary teeth have ID and OD faces, opposite axial end faces, andopposite circumferential end faces. The ID faces fall along a centralportion 38-1 of the gap 38. The OD portions may bear attachment featuresfor mounting to the back iron 60. An exemplary attachment feature 100 isa dovetail projection on the OD face of the tooth mating with a dovetailgroove or channel 102 in the ID surface of the back iron. Incombination, the teeth 64A, 64B, 66A, 66B may be designated as a centerlaminate. In some implementations, there may be a single center laminatesuch that, for example, an outer diameter portion is full annulus andthe teeth extend radially inward therefrom. Such an assembly could bemounted in the central back iron 60 by shrink fit (e.g., heating theback iron, sliding the laminate in and then cooling the back iron).

Axially outboard of the rings 50, 52 are respective end members. Theexemplary end members each comprise an outer diameter yoke 120, 122having an ID face, an OD face, and opposite axial end faces. An outboardaxial end face falls along the adjacent first or second end of thebearing 20. Each end member also comprises an end laminate. As with thecenter laminate, the exemplary end laminates are segmented into teeth134A, 134B, 136A, 136B (FIG. 6), and 138A, 138B, 140A, 140B (FIG. 4).Exemplary teeth geometry and attachments may be similar to thosedescribed above for the teeth of the center laminate. FIGS. 4 and 6 showrespective portions 38-3 and 38-2 of the gap 38 at the end laminates.

Returning to FIG. 1, the rotor comprises one or more first permanentmagnets 150 and one or more second permanent magnets 152, respectively,radially inboard of the stator permanent magnets 50 and 52 and ofrespective polarity substantially opposite thereto so as to cooperatewith the respective associated stator magnets to define the permanentmagnet flux loops associated with the permanent magnet bias discussedabove.

The exemplary stator comprises a metallic core 160 (e.g., of a magneticsteel) mounted to the shaft and carrying the stator permanent magnets inassociated radially outwardly open channels. For example, the supportmay be formed by turning of metallic rod stock on a lathe. In such anexemplary one piece support configuration, there are multiple of eachpermanent magnet 150, 152 forming respective circumferential arrays. Forexample, FIGS. 3 and 5 show examples of four end-to-end segments 152combining to surround a full 360°. Such a configuration of two or moremagnets allows assembly via radial inward insertion. In order toradially retain the magnets, the arrays may be contained by respectivejackets 170, 172. Exemplary jackets are non-metallic composite wrapping(e.g., carbon fiber or fiberglass tape in epoxy matrix).

FIG. 1 also shows the rotor as carrying a center laminate 178 andrespective first and second end laminates 180 and 182. These rotorlaminates are radially inboard of an axis aligned with the respectivestator laminates and define the associated gap portions 38-1, 38-2, and38-3 therewith.

The exemplary core 160 thus has respective portions 162, 164, and 166forming a rotor center back iron or yoke and first and second end backirons or yokes. In an alternative configuration, the core 160 ismultiple pieces. For example, one piece may form the center back ironand portions radially inboard of the rotor magnets and two respectivepieces may form the rotor end yokes. Such a configuration may allow easyassembly of a system with full annulus rotor magnets and no separateretainers. Assembly may be via a series of shrink fits via heating andcooling.

As is discussed further below, the inner diameter (ID) boundaries orfaces 179, 181, 183 of the rotor laminates are radially outboard of theID faces or boundaries 151, 153 of the rotor permanent magnets to easeturning of the flux fields. Specifically, FIG. 7 shows a schematiclongitudinal sectional view centrally through diametrically opposed pairof the center teeth and coils. In section, four flux loops 550A, 550B,552A, 552B are shown. These are shown schematically with a single lineeach rather than a plurality of lines each as in a contour map. Also,though one broken line path is shown through each laminate stack, itwould be a distribution of flux across the laminate stack. In FIG. 7,the coils are not energized. Thus, fields in the upper half of thedrawing are symmetric to those in the lower half.

FIG. 8 shows the fields as modified by electromagnetic bias of theradial coils to exert an upward force on the rotor as viewed in FIG. 8.Specifically, the illustrated coils are energized in such a direction sothat their associated magnetic flux augments the loops in the upper halfof the sheet and counters the loops in the lower half. The exemplarymagnitudes of applied currents are significant enough so that the netflux 550A′, 552A′ in the lower half is reversed in direction relative tothat of FIG. 7. Thus the upper flux loops 550B′, 552B′ are schematicallyshown of increased flux by greater line weight than in FIG. 7. The neteffect of this is to apply a force to the rotor in the upward directionalong the sheet.

Electrical hardware may comprise a traditional H-bridge for control ofcurrent in the coils 34A, 34B, 36A, 36B such as is disclosed in the WO'775 publication. FIG. 9 shows an H-bridge amplifier 840 used to powerone or more coils. This may be controlled by or integrated with thecontroller 200. In one example, each H-bridge amplifier 840 has a singleassociated coil and vice-versa. This allows independent powering of thecoils so that different current magnitudes may be applied to each. Theamplifier 840 has two legs or branches 841 and 842 connected in parallelto a voltage source 844. The exemplary voltage source 844 is a constantDC voltage source and may be shared by the H-bridge amplifiers of thedifferent coils.

The terminals 880 and 882 of the coil are connected across centrallocations of the two legs 841 and 842. To each side (high voltage andlow voltage) of each leg, the terminal 880, 882 is connected to thevoltage source via the parallel combination of a respective switchingdevice 851, 852, 853, 854 and diode 861, 862, 863, 864. Exemplaryswitching devices are gate controlled switching devices such asinsulated gate bipolar transistors (IGBT) or metal oxide field effecttransistors (MOSFET). As noted above, 880 and 882 may representterminals of an individual coil. Alternatively, the coils in a givenpair may be in series powered by a single H-bridge amplifier so that theterminal 880 is one terminal of the first coil, the terminal 882 is oneterminal of the second coil, and the other terminals of the coils areconnected to each other.

Alternative embodiments may have asymmetries between the coils of thetwo respective pairs or the two coils of a given pair. For example, itmay be desirable to provide a baseline upward bias. Also, yetalternative embodiments may have configurations other than the two pairs(e.g., three coils and associated teeth at 120° intervals).

FIG. 9 further shows a controller 200. The controller may be integratedwith or provided by a controller of the turbomachine (e.g. electriccompressor) as a whole or the system (e.g., refrigeration system). Thecontroller may receive user inputs from an input device (e.g., switches,keyboard, or the like) and sensors (not shown, e.g., pressure sensorsand temperature sensors at various system locations and, specificallyfor bearing control, radial position sensors (e.g., as shown in the WO'775 publication) and axial position sensors). The controller may becoupled to the sensors and controllable system components (e.g., valves,the bearings, the compressor motor, vane actuators, and the like) viacontrol lines (e.g., hardwired or wireless communication paths). Thecontroller may include one or more: processors; memory (e.g., forstoring program information for execution by the processor to performthe operational methods and for storing data used or generated by theprogram(s)); and hardware interface devices (e.g., ports) forinterfacing with input/output devices and controllable systemcomponents. Exemplary control is as disclosed in the WO '775publication.

FIGS. 10-12 show alternative bearings involving modifications to therotor. Stator and control details may be the same as discussed regardingthe bearing 20 of FIG. 1.

Relative to the rotor 22 of the bearing 20, the respective rotors 222,322, 422 of bearings 220, 320, 420 shift the rotor laminates somewhatradially inwardly and also shift outboard extremes of the rotor magnetsradially inwardly. The FIG. 10 rotor magnets 230, 232 are of generallytrapezoidal cross-section having parallel ID surfaces 231, 233 and ODapex surfaces. The OD apex surface is of shorter longitudinal spanleaving tapering end/OD (or axial outboard—relative to the magnet itselfrather than the bearing centerplane) surfaces (of identical half anglein the illustrated embodiment). The axial outboard surfaces thusradially inwardly converge in a respective outward axial direction fromthe magnet.

To accommodate the tapering end surfaces, the respective center laminatestack 240 and end laminate stacks 242 and 244 have individual laminatesof progressively changing ID along ID/end surfaces 241, 243, 245) sothat the center stack ID surface radially outwardly diverges in theoutward axial direction (away from the centerplane) and the end stack IDsurfaces 243, 245 radially inwardly converge in the outward axialdirection (away from the centerplane). Retainers or spacers 250, 252 mayencircle the magnets. Exemplary retainers or spacers are composites (asdescribed above) or a metal such as aluminum alloy or stainless steel(e.g., magnetic steel or other material is not required due to a lack ofkey flux paths passing through the retainers). Where the magnets 230 and232 are continuous, the spacers 230, 232 may primarily serve to maintainthe longitudinal integrity and positioning of the rotor laminates.

The example of the FIGS. 11 and 12 embodiments have similar rotorlaminate stacks and retainers/spacers to those of the rotor 222 of theFIG. 10 bearing 220. The magnets (or main magnets as discussed below)330, 332 are of rectangular half cross-section (with ID surfaces 331,333) axially co-extensive with the retainers/spacers. To fill gapsbetween the longitudinal ends of the magnets and the tapering IDsurfaces of the laminates, there are spacers 340, 342, 344, 346 of righttriangular half cross-section (thus forming frustoconical rings). Thesemay each be formed of a magnetic steel and may be continuous(single-piece) or segmented (multi-piece). The spacers facilitateturning of the flux fields which would not be efficiently accomplishedif the laminates, along their entire length, extended to or near thediameter of the magnet ID surface.

The FIG. 12 embodiment replaces the spacers 340, 342, 344, 346 withmagnets 440, 442, 444, 446 of similar shape. The magnets have polaritiesangled off axial (e.g. relatively close to halfway between axial andradial) to help turn the flux fields to transition between the rotorlaminates and the main rotor magnets 230, 232. Thus, the various magnetID surfaces 331, 333, 441, 443, 445, 447 are radially inboard ofadjacent laminate ID tapering surfaces.

Contrasted with different alternative prior art bearings, variousimplementations may have one or more of several advantages. The addedrotor magnets provide an additional flux boost. For example, in variousembodiments this boost may allow use of non-rare earth magnets. Thisreduces costs. Rare earth magnets are characterized by magnets with userare earth elements such as dysprosium, terbium, europium, neodymium,samarium, and yttrium. Combined contents of those elements willtypically be at least 10.0% by weight (e.g. 10.0% to 50.0%) or at least20.0%. Neodymium is typically the key element in the main class of rareearth magnets (neodymium magnets), thus non-rare earth magnets may haveunder 10.0% by weight of this element in particular. Another class issamarium-cobalt magnets (e.g. typically 15% to 45% samarium by weight)Thus, in non-rare earth magnets, samarium may also be below 15.0% or10.0% by weight. Exemplary non-rare earth magnets are ferrite/ceramicmagnets, alnico, manganese bismuth, iron nitride, and the like. However,other embodiments may use rare earth magnets or combinations.

The use of “first”, “second”, and the like in the description andfollowing claims is for differentiation within the claim only and doesnot necessarily indicate relative or absolute importance or temporalorder. Similarly, the identification in a claim of one element as“first” (or the like) does not preclude such “first” element fromidentifying an element that is referred to as “second” (or the like) inanother claim or in the description.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenapplied to an existing basic system, details of such configuration orits associated use may influence details of particular implementations.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A magnetic bearing (20; 220; 320; 420)comprising: a rotor (22; 222; 322; 422) to be supported for rotationabout an axis (502); a stator (24) extending from a first end (30) to asecond end (32) and comprising: one or more first permanent magnets(50); one or more second permanent magnets (52) axially spaced from theone or more first permanent magnets; a plurality of laminate teeth (64A,64B, 66A, 66B) axially between and extending radially inward of the oneor more first permanent magnets on one side and the one or more secondpermanent magnets on the other side; and a plurality of radial windingsrespectively encircling a respective associated tooth of the pluralityof teeth, wherein the rotor comprises: one or more third permanentmagnets (150; 230; 330); one or more fourth permanent magnets (152; 232;332) axially spaced from the one or more third permanent magnets; and acenter laminate (178; 240) axially between the one or more thirdpermanent magnets and the one or more fourth permanent magnets, thecenter laminate having an inner diameter (ID) surface radially outboardof respective inner diameter (ID) surfaces of the at least one thirdpermanent magnet and the at least one fourth permanent magnet.
 2. Themagnetic bearing of claim 1 wherein the one or more first permanentmagnets and the one or more second permanent magnets are non-rare earthmagnets.
 3. The magnetic bearing of claim 1 wherein the one or morethird permanent magnets and the one or more fourth permanent magnets arenon-rare earth magnets.
 4. The magnetic bearing of claim 1 wherein: theone or more second permanent magnets have a polarity substantiallyopposite to a polarity of the one or more first permanent magnets; andthe one or more fourth permanent magnets have a polarity substantiallyopposite to a polarity of the one or more third permanent magnets. 5.The magnetic bearing of claim 1 wherein: the one or more third permanentmagnets have a polarity substantially opposite to a polarity of the oneor more first permanent magnets; and the one or more fourth permanentmagnets have a polarity substantially opposite to a polarity of the oneor more second permanent magnets.
 6. The magnetic bearing of claim 1wherein the one or more first permanent magnets and the one or moresecond permanent magnets are full annulus.
 7. The magnetic bearing ofclaim 1 wherein the one or more third permanent magnets, the one or morefourth permanent magnets are circumferentially segmented.
 8. Themagnetic bearing of claim 1 being a non-thrust bearing.
 9. The magneticbearing of claim 1 wherein the stator further comprises: a center yoke(60) radially surrounding the plurality of teeth; a first end yoke (120)axially abutting the one or more first permanent magnets; and a secondend yoke (122) axially abutting the one or more second permanentmagnets.
 10. The magnetic bearing of claim 9 wherein the stator furthercomprises: a first end laminate (134A, 134B, 136A, 136B) encircled bythe first end yoke; and a second end laminate (138A, 138B, 140A, 140B)encircled by the second end yoke.
 11. The magnetic bearing of claim 1wherein the rotor further comprises: a first end laminate (180; 242)axially abutting the one or more third permanent magnets; and a secondend laminate (182; 244) axially abutting the one or more fourthpermanent magnets.
 12. The magnetic bearing of claim 11 wherein: therotor first end laminate (242) has an inner diameter surface radiallyinwardly converging in an outward axial direction; the rotor second endlaminate (244) has an inner diameter surface radially inwardlyconverging in an outward axial direction; and at least one of: the oneor more third permanent magnets (232) and one or more fourth permanentmagnets (230) have respective axial outboard surfaces radially inwardlyconverging in a respective outward axial direction; the rotor comprises:one or more first steel pieces (344) forming a frustoconical ringintervening between the one or more third permanent magnets and therotor first end laminate; and one or more second steel pieces (346)forming a frustoconical ring intervening between the one or more fourthpermanent magnets and the rotor second end laminate; and the rotorcomprises: one or more first end magnets (444) forming a frustoconicalring intervening between the one or more third permanent magnets and therotor first end laminate and having a less axial polarity than the oneor more third permanent magnets; and one or more second end magnets(446) forming a frustoconical ring intervening between the one or morefourth permanent magnets and the rotor second end laminate and having aless axial polarity than the one or more fourth permanent magnets.
 13. Amethod for using the magnetic bearing of claim 1, the method comprisingrunning current through: the plurality of radial windings, so as to:control radial position of the rotor.
 14. The method of claim 13wherein: the plurality of radial windings comprises a diametricallyopposite first pair of windings and a diametrically opposite second pairof windings orthogonal to the first pair of windings.
 15. The method ofclaim 14 wherein: the first and second pairs of windings are eachpowered by a respective associated H-bridge amplifier.
 16. A machinecomprising a bearing according to claim
 1. 17. A method for using amagnetic bearing, the magnetic bearing comprising: a rotor (22; 222;322; 422) to be supported for rotation about an axis (502); a stator(24) extending from a first end (30) to a second end (32) andcomprising: one or more first permanent magnets (50); one or more secondpermanent magnets (52) axially spaced from the one or more firstpermanent magnets; a plurality of laminate teeth (64A, 64B, 66A, 66B)axially between and extending radially inward of the one or more firstpermanent magnets on one side and the one or more second permanentmagnets on the other side; and a plurality of radial windingsrespectively encircling a respective associated tooth of the pluralityof teeth, wherein the rotor comprises: one or more third permanentmagnets (150; 230; 330); and one or more fourth permanent magnets (152:232; 332) axially spaced from the one or more third permanent magnets,the method comprising running current through the plurality of radialwindings, so as to control radial position of the rotor, wherein: theplurality of radial windings comprises a diametrically opposite firstpair of windings and a diametrically opposite second pair of windingsorthogonal to the first pair of windings; for each winding of the firstpair of windings and the second pair of windings: a first permanentmagnet flux paths passes as a loop through the winding, the at least onefirst permanent magnet and the at least one second permanent magnet; anda second permanent magnet flux paths passes as a loop through thewinding, the at least one second permanent magnet and the at least onefourth permanent magnet; and the running current comprises: runningcurrent through one winding of the first pair of windings to augment theassociated first and second permanent magnet flux paths while runningcurrent through the other winding of the first pair of windings tocounter the associated first and second permanent magnet flux paths. 18.The method of claim 17 wherein: the running current comprises: runningcurrent through one winding of the second pair of windings to augmentthe associated first and second permanent magnet flux paths whilerunning current through the other winding of the first pair of windingsto counter the associated first and second permanent magnet flux paths.19. A magnetic bearing (20; 220; 320; 420) comprising: a rotor (22; 222;322; 422) to be supported for rotation about an axis (502); a stator(24) extending from a first end (30) to a second end (32) andcomprising: one or more first permanent magnets (50); one or more secondpermanent magnets (52) axially spaced from the one or more firstpermanent magnets; a plurality of laminate teeth (64A, 64B, 66A, 66B)axially between and extending radially inward of the one or more firstpermanent magnets on one side and the one or more second permanentmagnets on the other side; and a plurality of radial windingsrespectively encircling a respective associated tooth of the pluralityof teeth, wherein the rotor comprises: one or more third permanentmagnets (150; 230; 330); one or more fourth permanent magnets (152; 232;332) axially spaced from the one or more third permanent magnets; acenter laminate (178; 240) axially between the one or more thirdpermanent magnets and the one or more fourth permanent magnets; a firstend laminate (180; 242) axially abutting the one or more third permanentmagnets; and a second end laminate (182; 244) axially abutting the oneor more fourth permanent magnets.
 20. The magnetic bearing of claim 19wherein: the rotor first end laminate (242) has an inner diametersurface radially inwardly converging in an outward axial direction; therotor second end laminate (244) has an inner diameter surface radiallyinwardly converging in an outward axial direction; and at least one of:the one or more third permanent magnets (232) and one or more fourthpermanent magnets (230) have respective axial outboard surfaces radiallyinwardly converging in a respective outward axial direction; the rotorcomprises: one or more first steel pieces (344) forming a frustoconicalring intervening between the one or more third permanent magnets and therotor first end laminate; and one or more second steel pieces (346)forming a frustoconical ring intervening between the one or more fourthpermanent magnets and the rotor second end laminate; and the rotorcomprises: one or more first end magnets (444) forming a frustoconicalring intervening between the one or more third permanent magnets and therotor first end laminate and having a less axial polarity than the oneor more third permanent magnets; and one or more second end magnets(446) forming a frustoconical ring intervening between the one or morefourth permanent magnets and the rotor second end laminate and having aless axial polarity than the one or more fourth permanent magnets. 21.The magnetic bearing of claim 19 wherein: the rotor first end laminate(242) has an inner diameter surface radially inwardly converging in anoutward axial direction; and the rotor second end laminate (244) has aninner diameter surface radially inwardly converging in an outward axialdirection.